Designing a least-cost scheme to drinking water from an estuary is a complex task when the water is to be supplied to a town or city close to the mouth of the estuary since the estuarine water is relatively saline in this region. The raw water intake must be sited to minimise the cost of capital works, which may include increased storage, while maintaining the salinity of water supplied to customers within acceptable limits. This is not a trivial exercise as flow in estuaries, i.e. where the river and ocean meet, is complicated by tides, winds, upstream river inflows, erosion, and the rotation of the earth resulting in a relatively complex system in which salinity can vary dramatically in time and space. In turn, the level of risk (of exceeding acceptable salinity in water supplied to the customer) varies depending upon the estuarine behaviour and factors, such as abstraction location, available water storage, and abstraction practice. Here we show, via a case study, how hydrology, hydraulics and economics must be integrated in order to find a least-cost solution that meets the needs of customers.

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